With the increasing drilling scale of oil and gas fields and the development of science and technology, especially the rapid development of a LWD technology, it is urgent to make the present advanced science and technology play an important role in the development of the oil and gas fields. An azimuthally acoustic LWD technology is one of LWD technologies, and an azimuthally acoustic while drilling transducer is one of the most important elements of an azimuthally acoustic while drilling instrument. During operation, a transmitting transducer built in the instrument generates acoustic waves. The acoustic waves are received by a receiving transducer in the same instrument. Properties of a reference medium are evaluated by means of acoustic information such as velocity and attenuation of various modes of the received waves. Since a fluid conduit through which mud passes is provided in the middle of the while drilling instrument, and an acoustic wave transducer is mounted on the outer wall of a drill collar body, which is immersed in oil and other fluids. As a wireline acoustic logging instrument, the azimuthally acoustic while drilling transducer is generally independently encapsulated. However, there are two types of azimuthally acoustic while drilling receiving transducers, namely, a button-shaped receiving transducer and an annularly-potted receiving transducer. The button-shaped receiving transducer is directly mounted in an electronic housing at a receiving end of the acoustic while drilling instrument. Such a transducer has a high sensitivity. The annularly-potted receiving transducer encapsulates multiple transducers into an annular ribbon structure, and a receiving chip is internally connected in parallel to form a receiving transducer. Such a receiving transducer is mainly used for a monopole azimuthally acoustic while drilling instrument.
The button-shaped receiving transducer encapsulating apparatus is configured as follows. A ceramic structure crystal is encapsulated into a button-shaped metal structure. The balance between mud external to a ceramic crystal plate and hydraulic oil internal to the ceramic sheet crystal is realized by means of a hydraulic balance apparatus in the button-shaped metal structure. The ceramic crystal plate needs to realize dynamic sealing in the button-shaped structure. That is, balancing the mud external to the ceramic crystal plate and the hydraulic oil internal to the ceramic crystal plate. Such a button-shaped receiving transducer is directly mounted on a frame of the electronic housing at the receiving end. Sealing of the mud external to the ceramic crystal plate and the electronic housing is realized by means of a sealing ring outside the button-shaped structure. Meanwhile, a dual-core electrical connection pin at the bottom of the transducer may realize a short-distance connection with a receiving circuit, so that a weak acoustic signal is received.
The annularly-potted receiving transducer encapsulating apparatus is realized as follows. A flake ceramic crystal plate structure is employed. A receiving chip is encapsulated into an annular ribbon. The receiving chip is internally connected in parallel to form a receiving transducer. An annular ribbon structure leads a chip signal receiving line out through a sealing structure and electrically connects two signal receiving lines with the internal electronic housing through a specially-designed sealing electrical connector. The transducer employing an epoxy resin potting sealant may be soaked in the mud, sealing the external mud and the internal electronic housing is realized by means of the specially-designed sealing electrical connector, so that a weak acoustic signal is received.
These two apparatuses respectively have disadvantages as explained in the following.
The button-shaped receiving transducer encapsulating apparatus increases the complexity of designing the transducer due to a requirement for a hydraulic dynamic balance design of the ceramic crystal plate and is susceptible to failure in use. The ceramic crystal plate of such a button-shaped transducer is exposed in the mud by adhering a layer of PEEK material on its outer surface, and is prone to damage in a downhole complex application environment; and because the transducer realizes high-pressure sealing with the drill collar body while being mounted on the frame of the internal electronic housing, such a structure increases requirements for machining and assembling the frame of the internal electronic housing and the external drill collar body; and
The annularly-potted receiving transducer encapsulating apparatus requires the specially-designed sealing electrical connector when being electrically connected with the internal housing for the electronics to meet requirements that the plug is in abut-joint with an electrical connector on the electronic circuit while realizing high-pressure sealing; meanwhile, it is required that the connector can be affixed to the drill collar body due to a downhole application environment with strong vibration shock; such an encapsulating structure on the one hand requires the specially-designed sealing connector, on the other hand increases requirements for machining and assembling the frame of the internal housing for the electronics and the external drill collar body; and furthermore, compared with the button-shaped transducer encapsulating structure, this structure increases the length of an electronic connection line from the transducer to the housing for electronics, which affects the signal extraction.